Adventitious

1. a. Acquired, as diseases; accidental.
2. a. Added extrinsically; not essentially inherent; accidental or causal; additional; supervenient; foreign.
3. a. Out of the proper or usual place; as, adventitious buds or roots.
4. a. Accidentally or sparingly spontaneous in a country or district; not fully naturalized; adventive; — applied to foreign plants.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.